Lens barrel

ABSTRACT

A lens barrel includes front and rear sub-lens groups; front and rear sub-lens group frames for supporting the front and rear sub-lens groups, respectively; a lens frame shift mechanism for causing the front sub-lens group frame and the rear sub-lens group frame to move relative to each other to obtain the mutually close position and the mutually distant position; a first lens group positioning surface provided on the front sub-lens group frame for positioning the front sub-lens group by contacting with a portion of a rear surface of the front sub-lens group; and a second lens group positioning surface provided on the rear sub-lens group frame for positioning the front sub-lens group by contacting with a portion of a front surface of the rear sub-lens group.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application relates to the following U.S. patentapplications, all filed concurrently herewith on Sep. 24, 2001, and allof which are expressly incorporated herein by reference in theirentireties: “ZOOM LENS MECHANISM” having U.S. patent application Ser.No. 09/960,309, “LENS DRIVE MECHANISM” having application Ser. No.09/960,382, “ECCENTRICITY-PREVENTION MECHANISM FOR A PAIR OFLENS-SUPPORTING RINGS” having application Ser. No. 09/960,515,“REDUCTION GEAR MECHANISM” having application Ser. No. 09/960,521, “RINGMEMBER SHIFT MECHANISM AND LENS GROUP SHIFT MECHANISM” havingapplication Ser. No. 09/960,518, “LENS BARREL” having application Ser.No. 09/960,382, “LENS BARREL” having application Ser. No. 09/960,516,“LENS BARREL” having application Ser. No. 09/961,233, “ZOOM LENS BARREL”having application Ser. No. 09/961,185, and “LENS BARREL” havingapplication Ser. No. 09/961,232, each naming as inventors Hiroshi NOMURAet al.; and “LENS DRIVE CONTROL APPARATUS FOR ZOOM LENS SYSTEM HAVING ASWITCHING LENS GROUP” having application Ser. No. 09/961,186 and namingas inventor Norio NUMAKO.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a lens barrel and, more particularly,to a lens barrel supporting a pair of sub-lens groups, functioningoptically when in a mutually close position and in a mutually distantposition.

2. Description of the Related Art

In a lens barrel constructed to support a plurality of lens groups,distances between the lens groups must be accurate. This is difficultbecause the distance between the lens groups is affected not only by theaccuracy of the lens itself but also by the accuracy of assemblyprocesses of the lens group frames. Accordingly, the lens distance tendto deviate from one lens barrel to another. While this deviation in thedistances may be avoided by providing an adjustment mechanism, provisionof such additional mechanisms inevitably leads to larger construction ofthe lens barrel and an increase in manufacturing costs. Also, adjustingactual distances in each lens barrel is inefficient.

For example, the assignee of the present application has proposed anunprecedented zoom lens system that meets the contradictory demands ofhigh zoom ratio and miniaturization (U.S. patent application Ser. No.09/534,307, Japanese Patent Application No. Hei 11-79572). This zoomlens system has the following characteristics: it includes a pluralityof movable lens groups for varying the focal length; at least one of thelens groups is a switching lens group which includes two sub-lensgroups, one of the sub-lens groups being a movable sub-lens group thatcan be selectively positioned at either one movement extremities in theoptical axis direction with respect to the other sub-lens group; themovable sub-lens group of the switching lens group is positioned at anextremity of a short-focal-length zooming range, from the short focallength extremity to an intermediate focal length, and at the oppositeextremity of a long-focal-length zooming range, from the intermediatefocal length to a long focal length extremity; and zoom paths of theswitching lens group and the other lens groups are discontinuous at theintermediate focal length and are defined to focus on a predeterminedimage plane corresponding to the position of the movable sub-lens group.There may be one or more intermediate focal lengths.

In the mechanical structure of the lens barrel for use in such a zoomlens system, it is desirable to prevent deviation in distance betweenthe sub-lens groups without using an adjustment mechanism in order toavoid a large and complicated switching lens group unit construction,since mechanisms for moving the sub-lens groups toward and away fromeach other are provided in the support barrel for the switching lensgroup, which forms a single lens group.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to achieve a lensbarrel having a simple construction that can prevent deviation in thedistance between the first sub-lens group and the second sub-lens group,wherein the first and second sub-lens groups function optically when ina mutually close position and in a mutually distant position.

In order to achieve the above-mentioned object, a lens barrel includes afront sub-lens group provided on the object side and a rear sub-lensgroup provided on the image side, the front and rear sub-lens groupsfunctioning optically when in a mutually close position and in amutually distant position with respect to the optical axes of the frontand rear sub-lens groups; a front sub-lens group frame for supportingthe front sub-lens group and a rear sub-lens group frame for supportingthe rear sub-lens group, the front and rear sub-lens group frames beingheld in engagement with each other while being able to move in theoptical axis direction relative to each other; a lens frame shiftmechanism for causing the front sub-lens group frame and the rearsub-lens group frame to move relative to each other to obtain themutually close position and the mutually distant position; a first lensgroup positioning surface, provided on the front sub-lens group frame,for positioning the front sub-lens group in the optical axis directionby contacting a portion of a rear surface of the front sub-lens groupupon the front sub-lens group being inserted from the front side of thefront sub-lens group frame; and a second lens group positioning surface,provided on the rear sub-lens group frame, for positioning the rearsub-lens group in the optical axis direction by contacting a portion ofa front surface of the rear sub-lens group upon the rear sub-lens groupbeing inserted from the rear side of the rear sub-lens group frame.

In an embodiment, the front sub-lens group frame includes a front sealedregion in the front end portion thereof, the front sealed regionpreventing the front sub-lens group from coming out from the front sideof the front sub-lens group frame. The rear sub-lens group frameincludes a rear sealed region in the rear end portion thereof, the rearsealed region preventing the rear sub-lens group from coming out fromthe rear side of the front sub-lens group frame.

Preferably, the lens barrel further includes a pair of follower engagingrecesses which are formed on one of opposing surfaces of the frontsub-lens group frame and the rear sub-lens group frame; and a followerprojection which are formed on the other of the opposing surfaces of thefront sub-lens group frame and the rear sub-lens group frame. Themutually close position of the front sub-lens group is defined viaengagement of the follower projection and one of the pair of followerengaging recesses, and the mutually distant position of the frontsub-lens group is defined via engagement of the follower projection andthe other of the pair of follower engaging recesses.

Preferably, the front sub-lens group frame and the rear sub-lens groupframe can be rotated relative to each other. The lens frame shiftmechanism includes a shift cam mechanism provided on opposing surfacesof the front sub-lens group frame and the rear sub-lens group frame formoving the front and rear sub-lens group frames to the mutually distantposition and to the mutually close position in accordance with therelative rotation of the front and rear sub-lens group frames.

Preferably, the shift cam mechanism includes a shift cam surfaceprovided on one of the opposing surfaces of the front sub-lens groupframe and the rear sub-lens group frame, the shift cam surface beinginclined with respect to a circumferential direction thereof; and afollower projection provided on the other of the opposing surfaces ofthe front sub-lens group frame and the rear sub-lens group frame forengaging with the shift cam surface.

Preferably, a pair of follower engaging recesses are formed at oppositeends of each of the shift cam surfaces, wherein the follower projectionengages with one of the follower engaging recesses when the front andrear sub-lens group frames are in the mutually close position and in themutually distant position.

Preferably, the front and rear sub-lens groups form one of a pluralityof variable lens groups of a zoom lens system that are moved in theoptical axis direction during zooming, the front and rear sub-lensgroups serving as a focusing lens group when in the mutually closeposition and in the mutually distant position. The lens barrel includesa focusing mechanism for moving the front and rear sub-lens group framesin the mutually close position and in the mutually distant position, inthe optical axis direction, while maintaining a constant distancebetween the front and rear sub-lens group frames.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2000-289388 (filed on Sep. 22, 2000) which isexpressly incorporated herein in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a first embodiment of a zoom lenssystem having switching lens groups and the fundamental zoom paththereof, to which the present invention is applied.

FIG. 2 is a schematic drawing of a second embodiment of a zoom lenssystem having switching lens groups and the fundamental zoom paththereof, to which the present invention is applied.

FIG. 3 is a schematic drawing of a third embodiment of a zoom lenssystem having switching lens groups and the fundamental zoom paththereof, to which the present invention is applied.

FIG. 4 is a schematic drawing of a fourth embodiment of a zoom lenssystem having switching lens groups and the fundamental zoom paththereof, to which the present invention is applied.

FIG. 5 is a schematic drawing of a fifth embodiment of a zoom lenssystem having switching lens groups and the fundamental zoom paththereof, to which the present invention is applied.

FIG. 6 is a schematic drawing of a sixth embodiment of a zoom lenssystem having switching lens groups and the fundamental zoom paththereof, to which the present invention is applied.

FIG. 7 is a schematic drawing of a seventh embodiment of a zoom lenssystem having switching lens groups and the fundamental zoom paththereof, to which the present invention is applied.

FIG. 8 shows one example of stopping positions of the lens groups when aphotographic operation is carried out, to which the present invention isapplied.

FIG. 9A shows an example of the stopping positions of FIG. 8 and anexample of an actual zoom path of the lens groups, to which the presentinvention is applied.

FIGS. 9B and 9C depict an additional schematic view of the conceptsshown in FIGS. 8 and 9A.

FIG. 10 is a cross-sectional view showing an embodiment of a zoom lensbarrel which includes the zoom lens systems having switching lens groupsshown in FIGS. 1, 8 and 9.

FIG. 11 is a developed view of an inner surface of a cam ring of thezoom lens barrel of FIG. 10 showing an exemplary arrangement of camgrooves.

FIG. 12 is an exploded perspective view showing components of aswitching lens group frame of the zoom lens barrel.

FIG. 13 is an exploded perspective view showing some of the componentsof the switching lens group frame of the zoom lens barrel.

FIG. 14 is a perspective view showing a different assembly of some ofthe components of the switching lens group frame of the zoom lensbarrel.

FIG. 15 is a cross-sectional view of an upper half of the switching lensgroup in which a first sub-lens group and a second sub-lens group are ina mutually distant position at the wide-angle extremity.

FIG. 16 is a cross-sectional view of an upper half of the switching lensgroup in which the first sub-lens group and the second sub-lens groupare in a mutually close position at the telephoto extremity.

FIG. 17A is an exploded view in which components are exploded in theoptical axis direction, wherein the first sub-lens group and the secondsub-lens group are in the mutually distant position at the wide-angleside and are focused on an object at infinity.

FIG. 17B is a developed view showing the components of FIG. 17A inactual engagement.

FIG. 18A is an exploded view in which components are exploded in theoptical axis direction, wherein the first sub-lens group and the secondsub-lens group are in the mutually distant position at the wide-angleside and are focused on an object at a minimum distance.

FIG. 18B is a developed view showing the components of FIG. 18A inactual engagement.

FIG. 19A is an exploded view in which components are exploded in theoptical axis direction, wherein the first sub-lens group and the secondsub-lens group are in the mutually close position at the telephoto sideand are focused on an object at infinity.

FIG. 19B is a developed view showing the components of FIG. 19A inactual engagement.

FIG. 20A is an exploded view in which components are exploded in theoptical axis direction, wherein the first sub-lens group and the secondsub-lens group are in the mutually close position at the telephoto sideand are focused on an object at a minimum distance.

FIG. 20B is a developed view showing the components of FIG. 20A inactual engagement.

FIG. 21 is an exploded view illustrating how the mutually close positionof the first sub-lens group and the second sub-lens group on thetelephoto side switches to/from the mutually distant position on thewide-angle side via the rotation of an actuator ring.

FIG. 22 illustrates how focusing is carried out by the actuator ring.

FIG. 23 is an enlarged expanded view showing a face cam of a firstsub-lens group frame.

FIG. 24 is an enlarged developed view showing the relationship of thefirst sub-lens group frame, the second sub-lens group frame, and theactuator ring with respect to a front shutter retaining ring.

FIG. 25 is a front view showing the relationship between the firstsub-lens group frame and the front shutter retaining ring when viewed ina direction of the arrows indicated by a line XXV—XXV in FIG. 14.

FIG. 26 is a partially enlarged view showing an encircled portionindicated by XXVI in FIG. 25.

FIG. 27 is a front view showing the relationship between the secondsub-lens group frame and the front shutter retaining ring when viewed ina direction of the arrows indicated by the line XXVII—XXVII in FIG. 14.

FIG. 28 is a partially enlarged view showing an encircled part XXVIII inFIG. 27.

FIG. 29 is a front view showing an arrangement of reduction gears of adriving system of the actuator ring, the reduction gears being retainedbetween the front shutter retaining ring and the gear holding ring.

FIG. 30 is a developed plan view of FIG. 29.

FIG. 31 is a block diagram showing a control system of the zoom lensbarrel shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the embodiment described below, the present invention is applied to alens barrel. This lens barrel is suitable for use with a zoom lenssystem proposed by the assignee of the present application in the U.S.patent application Ser. No. 09/534,307. U.S. patent application Ser. No.09/534,307 is expressly incorporated herein by reference in itsentirety.

First, embodiments of a zoom lens system with a switching lens groupproposed in the U.S. patent application Ser. No. 09/534,307 will beherein described.

FIG. 1 shows the first embodiment of the zoom lens system. The zoom lenssystem includes a positive first variable lens group 10, and a negativesecond variable lens group 20, in that order from the object side. Thefirst variable lens group 10 includes a negative first lens group L1(first sub-lens group S1) and a positive second lens group L2 (secondsub-lens group S2), in that order from the object side. The secondvariable lens group 20 includes a negative third lens group L3. Thesecond sub-lens group S2 of the first variable lens group 10 is fixed toa first lens group frame 11. The first sub-lens group S1 is mounted on amovable sub-lens group frame 12. The movable sub-lens group frame 12 isarranged to move in the optical axis direction, by a predetermineddistance, along a guide groove 13 which is formed on the first lensgroup frame 11. The first sub-lens group S1 is selectively moved toeither the object-side movement extremity at which the movable sub-lensgroup frame 12 comes into contact with the front end of the guide groove13, or the image-side movement extremity at which the movable sub-lensgroup frame 12 comes into contact with the rear end of the guide groove13. The third lens group L3 is fixed to a second lens group frame 21. Adiaphragm D is arranged to move together with the first variable lensgroup 10 (first lens group frame 11). Throughout FIGS. 1 through 9, IMindicates an image plane (film surface, and so forth) which is at apredetermined position.

In the zoom paths according to the first embodiment, the first variablelens group 10 (first lens group frame 11), the second variable lensgroup 20 (second lens group frame 21), and the first sub-lens group S1(movable sub-lens group frame 12) move in the following manner:

[A] In a short-focal-length zooming range Zw from the short focal lengthextremity fw to an intermediate focal length fm, the first sub-lensgroup S1 and the second sub-lens group S2 maintain a distance d1therebetween (first separation space/wide space); and the first variablelens group 10 (first lens group frame 11) and the second variable lensgroup 20 (second lens group frame 21) move towards the object side whilemutually changing the distance therebetween.

[B] At the intermediate focal length fm, the first variable lens group10 and the second variable lens group 20 move towards the image side atthe long focal-length extremity of the short-focal-length zooming rangeZw; and the first sub-lens group S1 moves to the image-side movementextremity of the guide groove 13, wherein the first sub-lens group S1moves toward the second sub-lens group S2 so that the distancetherebetween is determined by a shorter distance (second separationspace/narrow space) d2.

[C] In a long-focal-length zooming range Zt from the intermediate focallength fm to the long focal length extremity ft, the first sub-lensgroup S1 maintains the shorter distance (second separation space/narrowspace) d2 with respect to the second sub-lens group S2; and the firstvariable lens group 10 and the second variable lens group 20 movetowards the object, based on the positions thereof which are determinedat the intermediate focal length fm, after the first through third lensgroups L1 through L3 have been moved towards the image side, whilechanging the distance therebetween.

The zoom paths for the first variable lens group 10 and the secondvariable lens group 20 are simply depicted as straight lines in FIG. 1.It should be noted, however, that the actual zoom paths are notnecessarily straight lines.

Focusing is performed by integrally moving, in the optical axisdirection, the first sub-lens group S1 and the second sub-lens group S2,i.e., the first variable lens group 10 (first lens group frame 11)regardless of the zooming range.

FIG. 2 shows the second embodiment of the zoom lens system. The zoomlens system includes a positive first variable lens group 10, a positivesecond variable lens group 20, and a negative third variable lens group30, in that order from the object side. The first variable lens group 10includes a positive first lens group L1. The second variable lens group20 includes a negative second lens group L2 (first sub-lens group S1)and a positive third lens group L3 (second sub-lens group S2), in thatorder from the object side. The third variable lens group 30 includes anegative fourth lens group L4. The first lens group L1 is fixed to afirst lens group frame 11. The second sub-lens group S2 of the secondvariable lens group 20 is fixed to a second lens group frame 21. Thefirst sub-lens group S1 is mounted on a movable sub-lens group frame 22.The movable sub-lens group frame 22 is arranged to move, in the opticalaxis direction, by a predetermined distance, along a guide groove 23which is formed on the second lens group frame 21. The first sub-lensgroup S1 is selectively moved to either the object-side movementextremity at which the movable sub-lens group frame 22 comes intocontact with the front end of the guide groove 23, or the image-sidemovement extremity at which the movable sub-lens group frame 22 comesinto contact with the rear end of the guide groove 23. The fourth lensgroup L4 is fixed to a third lens group frame 31. A diaphragm D isarranged to move together with the second variable lens group 20 (secondlens group frame 21).

In the zoom paths according to the second embodiment, the first variablelens group 10 (first lens group frame 11) the second variable lens group20 (second lens group frame 21), the third variable lens group 30 (thirdlens group frame 31), and the first sub-lens group S1 (movable sub-lensgroup frame 22) move in the following manner:

[A] In a short-focal-length zooming range Zw from the short focal lengthextremity fw to an intermediate focal length fm, the first sub-lensgroup S1 and the second sub-lens group S2 maintain a distance d1 (firstseparation space/wide space); and the first variable lens group 10(first lens group frame 11), the second variable lens group 20 (secondlens group frame 21) and the third variable lens group 30 (third lensgroup frame 31) move towards the object side while mutually changing thedistances therebetween.

[B] At the intermediate focal length fm, the first variable lens group10, the second variable lens group 20 and the third variable lens group30 are moved towards the image side at the long focal-length extremityof the short-focal-length zooming range Zw; and the first sub-lens groupS1 moves to the image-side movement extremity of the guide groove 23,wherein the first sub-lens group S1 moves toward the second sub-lensgroup S2 so that the distance therebetween is determined by a shorterdistance (second separation space/narrow space) d2.

[C] In a long-focal-length zooming range Zt from the intermediate focallength fm to the long focal length extremity ft, the first sub-lensgroup S1 and the second sub-lens group S2 maintain the shorter distanced2; and the first variable lens group 10, the second variable lens group20 and third variable lens group 30 move towards the object side basedon the positions thereof which are determined at the intermediate focallength fm, after the first through fourth lens groups 1 through 4 havebeen moved towards the image side, while changing the distancestherebetween.

The zoom paths for the first variable lens group 10, the second variablelens group 20 and the third variable lens group 30 are simply depictedas straight lines in FIG. 2. It should be noted, however, that actualzoom paths are not necessarily straight lines.

Focusing is performed by integrally moving, in the optical axisdirection, the first sub-lens group S1 and the second sub-lens group S2,i.e., the second variable lens group 20 (second lens group frame 21)regardless of the zooming range.

Likewise with the first embodiment, the zoom paths are discontinuous atthe intermediate focal length fm; however, a solution for continuouslyforming a correct image plane exists by appropriately determining thepositions of the first lens group L1, the first sub-lens group S1(second lens group L2) and the second sub-lens group S2 (third lensgroup L3) and the fourth lens group L4 respectively at the short focallength extremity fw, the intermediate focal length fm (discontinuousline) and the long focal length extremity ft. According to such a zoompath, a miniaturized zoom lens system having a high zoom ratio can beobtained.

FIG. 3 shows the third embodiment of the zoom lens system with aswitching lens system. In this embodiment, the first lens group L1 isconstructed so as to have negative refractive power, which is the onlydifference compared with the second embodiment. Apart from thischaracteristic, the third embodiment is substantially the same as thesecond embodiment.

FIG. 4 shows the fourth embodiment of the zoom lens system with aswitching lens group. The zoom lens system includes a positive firstvariable lens group 10, and a negative second variable lens group 20, inthat order from the object side. The first variable lens group 10includes a negative first lens group L1 (first sub-lens group S1) and apositive second lens group L2 (second sub-lens group S2) in that orderfrom the object side. The second variable lens group 20 includes apositive third lens group L3 (third sub-lens group S3) and a negativefourth lens group L4 (fourth sub-lens group S4), in that order from theobject side.

The second sub-lens group S2 of the first variable lens group 10 isfixed to a first lens group frame 11. The first sub-lens group S1 ismounted on a movable sub-lens group frame 12. The movable sub-lens groupframe 12 is arranged to move in the optical axis direction, by apredetermined distance, along a guide groove 13 which is formed on thefirst lens group frame 11. The first sub-lens group S1 is selectivelymoved to either the object-side movement extremity at which the movablesub-lens group frame 12 comes into contact with the front end of theguide groove 13, or the image-side movement extremity at which themovable sub-lens group frame 12 comes into contact with the rear end ofthe guide groove 13. Similarly, the fourth sub-lens group S4 of thesecond variable lens group 20 is fixed to a second lens group frame 21.The third sub-lens group S3 is mounted on a movable sub-lens group frame22. The movable sub-lens group frame 22 is arranged to move in theoptical axis direction, by a predetermined distance, along a guidegroove 23 which is formed on the second lens group frame 21. The thirdsub-lens group S3 is selectively moved to either the object-sidemovement extremity at which the movable sub-lens group frame 22 comesinto contact with the front end of the guide groove 23, or theimage-side movement extremity at which the movable sub-lens group frame22 comes into contact with the rear end of the guide groove 23. Adiaphragm D is arranged to move together with the first variable lensgroup 10 (first lens group frame 11).

In the zoom paths according to the fourth embodiment, the first variablelens group 10 (first lens group frame 11), the second variable lensgroup 20 (second lens group frame 21), the first sub-lens group S1, andthe third sub lens group S3 move in the following manner:

[A] In a short-focal-length zooming range Zw from the short focal lengthextremity fw to an intermediate focal length fm, the first sub-lensgroup S1 and the second sub-lens group S2 maintain a distance d1therebetween (first separation space/wide space), and the third sub-lensgroup S3 and the fourth sub-lens group S4 maintain a distance d3therebetween (first separation space/wide space); and the first variablelens group 10 (first lens group frame 11) and the second variable lensgroup 20 (second lens group frame 21) move towards the object side whilemutually changing the distance therebetween.

[B] At the intermediate focal length fm, the first variable lens group10 and the second variable lens group 20 are moved towards the imageside at the long focal-length extremity of the short-focal-lengthzooming range Zw; and the first sub-lens group S1 moves to theimage-side movement extremity of the guide groove 13, wherein the firstsub-lens group S1 moves toward the second sub-lens group S2 so that thedistance therebetween is determined by a shorter distance (secondseparation space/narrow space) d2, and also the third sub-lens group S3moves toward the fourth sub-lens group S4 so that the distancetherebetween is determined by a shorter distance (second separationspace/narrow space) d4.

[C] In a long-focal-length zooming range Zt from the intermediate focallength fm to the long focal length extremity ft, the first sub-lensgroup S1 and the second sub-lens group S2 maintain the shorter distanced2 therebetween, and the third sub-lens group S3 and the fourth sub-lensgroup S4 maintain the shorter distance d4 therebetween; and the firstvariable lens group 10 and the second variable lens group 20 movetowards the object side based on the positions thereof which aredetermined at the intermediate focal length fm, after the first throughfourth lens groups L1 through L4 have been moved towards the image side,while changing the distance therebetween.

The zoom paths for the first variable lens group 10 and the secondvariable lens group 20 are simply depicted as straight lines in FIG. 4.It should be noted, however, that the actual zoom paths are notnecessarily straight lines.

Focusing is performed by integrally moving, in the optical axisdirection, the first sub-lens group S1 and the second sub-lens group S2,i.e., the first variable lens group 10 (first lens group frame 11)regardless of the zooming range.

Similar to the first through third embodiments, in the fourthembodiment, the zoom paths are discontinuous at the intermediate focallength fm; however, a solution for continuously forming a correct imageplane exists by appropriately determining the positions of the firstsub-lens group S1 (first lens group L1), the second sub-lens group S2(second lens group L2), the third sub-lens group S3 (third lens groupL3), and the fourth sub-lens group S4 (fourth lens group L4),respectively, at the short focal length extremity fw, the intermediatefocal length fm (discontinuous line), and the long focal lengthextremity ft. According to such a zoom path, a miniaturized zoom lenssystem having a high zoom ratio can be obtained.

FIG. 5 shows the fifth embodiment of the zoom lens system with aswitching lens group. The zoom lens system includes a positive firstvariable lens group 10, and a negative second variable lens group 20, inthat order from the object side. The first variable lens group 10includes a negative first lens group L1 (first sub-lens group S1) and apositive second lens group L2 (second sub-lens group S2), in that orderfrom the object side. The second variable lens group 20 includes apositive third lens group L3 (third sub-lens group S3) and a negativefourth lens group L4 (fourth sub-lens group S4), in that order from theobject side.

The second sub-lens group S2 of the first variable lens group 10 isfixed to a first lens group frame 11. The first sub-lens group S1 ismounted on a movable sub-lens group frame 12. The movable sub-lens groupframe 12 is arranged to move in the optical axis direction, by apredetermined distance, along a guide groove 13 which is formed on thefirst lens group frame 11. The first sub-lens group S1 is selectivelymoved to either the object-side movement extremity at which the movablesub-lens group frame 12 comes into contact with the front end of theguide groove 13, or the image-side movement extremity at which themovable sub-lens group frame 12 comes into contact with the rear end ofthe guide groove 13. Similarly, the fourth sub-lens group S4 of thesecond variable lens group 20 is fixed to a second lens group frame 21.The third sub-lens group S3 is mounted on a movable sub-lens group frame22. The movable sub-lens group frame 22 is arranged to move in theoptical axis direction, by a predetermined distance, along a guidegroove 23 which is formed on the second lens group frame 21. The thirdsub-lens group S3 is selectively moved to either the object-sidemovement extremity at which the movable sub-lens group frame 22 comesinto contact with the front end of the guide groove 23, or theimage-side movement extremity at which the movable sub-lens group frame22 comes into contact with the rear end of the guide groove 23. Adiaphragm D is arranged to move together with the first variable lensgroup 10 (first lens group frame 11).

In the zoom paths according to the fifth embodiment, the first variablelens group 10 (first lens group frame 11), the second variable lensgroup 20 (second lens group frame 21), the first sub-lens group S1, andthe third sub lens group S3 move in the following manner:

[A] In a short-focal-length zooming range Zw from the short focal lengthextremity fw to a first intermediate focal length fm1, the firstsub-lens group S1 and the second sub-lens group S2 maintain a distanced1 therebetween (first separation space/wide space), and the thirdsub-lens group S3 and the fourth sub-lens group S4 maintain a distanced3 therebetween (first separation space/wide space); and the firstvariable lens group 10 (first lens group frame 11) and the secondvariable lens group 20 (second lens group frame 21) move towards theobject side while mutually changing the distance therebetween.

[B] At the first intermediate focal length fm1, the first variable lensgroup 10 and the second variable lens group 20 are moved towards theimage side at the long focal-length extremity of the short-focal-lengthzooming range Zw; and the first sub-lens group S1 moves to theimage-side movement extremity of the guide groove 13, wherein the firstsub-lens group S1 moved toward the second sub-lens group S2 so that thedistance therebetween is determined by a shorter distance (secondseparation space/narrow space) d2.

[C] In an intermediate zooming range Zm from the first intermediatefocal length fm1 to a second intermediate focal length fm2, the firstsub-lens group S1 and the second sub-lens group S2 maintain the shorterdistance d2, and the third sub-lens group S3 and the fourth sub-lensgroup S4 maintain the longer distance d3; and the first variable lensgroup 10 and the second variable lens group 20 move towards the objectside based on the positions thereof which are determined at the firstintermediate focal length fm1, after the first through fourth lensgroups L1 through L4 have been moved towards the image side, whilechanging the distance therebetween.

[D] At the second intermediate focal length fm2, the first variable lensgroup 10 and the second variable lens group 20 are moved towards theimage side at the long focal length extremity of the intermediatezooming range Zm; and the third sub-lens group S3 moves to theimage-side movement extremity of the guide groove 23, wherein the thirdsub-lens group S3 moves toward the fourth sub-lens group S4 so that thedistance therebetween is determined by a shorter distance (secondseparation space/narrow space) d4.

[E] In a long-focal-length zooming range Zt from the second intermediatefocal length fm2 to the long focal length extremity ft, the firstsub-lens group S1 and the second sub-lens group S2 maintain the shorterdistance d2 therebetween, and the third sub-lens group S3 and the fourthsub-lens group S4 maintain the shorter distance d4 therebetween; and thefirst variable lens group 10 and the second variable lens group 20 movetowards the object side based on the positions thereof which aredetermined at the second intermediate focal length fm2, after the firstthrough fourth lens groups L1 through L4 have been moved towards theimage side, while changing the distance therebetween.

The zoom paths for the first variable lens group 10 and the secondvariable lens group 20 are simply depicted as straight lines in FIG. 5.It should be noted, however, that the actual zoom paths are notnecessarily straight lines.

Focusing is performed by integrally moving, in the optical axisdirection, the first sub-lens group S1 and the second sub-lens group S2,i.e., the first variable lens group 10 (first lens group frame 11)regardless of the zooming range.

Similar to the first through fourth embodiments, in the fifthembodiment, the zoom paths are discontinuous at the first intermediatefocal length fm1 and the second intermediate focal length fm2; however,a solution for continuously forming a correct image plane exists byappropriately determining the positions of the first sub-lens group S1(first lens group L1), the second sub-lens group S2 (second lens groupL2), the third sub-lens group S3 (third lens group L3) and the fourthsub-lens group S4 (fourth lens group L4), respectively, at the shortfocal length extremity fw, the first and second intermediate focallengths fm1, fm2 (discontinuous line), and the long focal lengthextremity ft. According to such a zoom path, a miniaturized zoom lenssystem having a high zoom ratio can be obtained.

FIG. 6 shows the sixth embodiment of the zoom lens system with aswitching lens group. The zoom lens system includes a positive firstvariable lens group 10, and a negative second variable lens group 20, inthat order from the object side. The first variable lens group 10includes a negative first lens group L1 (first sub-lens group S1) and apositive second lens group L2 (second sub-lens group S2), in that orderfrom the object side. The second variable lens group 20 includes apositive third lens group L3 (third sub-lens group S3) and a negativefourth lens group L4 (fourth sub-lens group S4), in that order from theobject side.

The second sub-lens group S2 of the first variable lens group 10 isfixed to a first lens group frame 11. The first sub-lens group S1 ismounted on a movable sub-lens group frame 12. The movable sub-lens groupframe 12 is arranged to move in the optical axis direction, by apredetermined distance, along a guide groove 13 which is formed on thefirst lens group frame 11. The first sub-lens group S1 is selectivelymoved to either the object-side movement extremity at which the movablesub-lens group frame 12 comes into contact with the front end of theguide groove 13, or the image-side movement extremity at which themovable sub-lens group frame 12 comes into contact with the rear end ofthe guide groove 13. Similarly, the fourth sub-lens group S4 of thesecond variable lens group 20 is fixed to a second lens group frame 21.The third sub-lens group S3 is mounted on a movable sub-lens group frame22. The movable sub-lens group frame 22 is arranged to move in theoptical axis direction, by a predetermined distance, along a guidegroove 23 which is formed on the second lens group frame 21. The thirdsub-lens group S3 is selectively moved to either the object-sidemovement extremity at which the movable sub-lens group frame 22 comesinto contact with the front end of the guide groove 23, or theimage-side movement extremity at which the movable sub-lens group frame22 comes into contact with the rear end of the guide groove 23. Adiaphragm D is arranged to move together with the first variable lensgroup 10 (first lens group frame 11).

In the zoom paths according to the sixth embodiment, the first variablelens group 10 (first lens group frame 11), the second variable lensgroup 20 (second lens group frame 21), the first sub-lens group S1, andthe third sub lens group S3 move in following manner:

[A] In a short-focal-length zooming range Zw from the short focal lengthextremity fw to a first intermediate focal length fm1, the firstsub-lens group S1 and the second sub-lens group S2 maintain a distanced1 therebetween (first separation space/wide space), and the thirdsub-lens group S3 and the fourth sub-lens group S4 maintain a distanced3 therebetween (first separation space/wide space); and the firstvariable lens group 10 (first lens group frame 11) and the secondvariable lens group 20 (second lens group frame 21) move towards theobject side while mutually changing the distance therebetween.

[B] At the first intermediate focal length fm1, the first variable lensgroup 10 and the second variable lens group 20 are moved towards theimage side at the long focal length extremity of the short-focal-lengthzooming range Zw; and the third sub-lens group S3 moves to theimage-side movement extremity of the guide groove 23, and wherein thethird sub-lens group S3 moves toward the fourth sub-lens group S4 sothat the distance therebetween is determined by a shorter distance(second separation space/narrow space) d4.

[C] In an intermediate zooming range Zm from the first intermediatefocal length fm1 to a second intermediate focal length fm2, the firstsub-lens group S1 and the second sub-lens group S2 maintain the longerdistance d1 therebetween, and the third sub-lens group S3 and the fourthsub-lens group S4 maintain the shorter distance d4 therebetween; and thefirst variable lens group 10 and the second variable lens group 20 movetowards the object side based on the positions thereof which aredetermined at the first intermediate focal length fm1, after the firstthrough fourth lens groups L1 through L4 have been moved towards theimage side, while changing the distance therebetween.

[D] At the second intermediate focal length fm2, the first variable lensgroup 10 and the second variable lens group 20 are moved towards theimage side at the long focal length extremity of the intermediatezooming range Zm; and the first sub-lens group S1 moves to theimage-side movement extremity of the guide groove 13, and wherein thefirst sub-lens group S1 moves toward the second sub-lens group S2 sothat the distance therebetween is determined by a shorter distance(second separation space/narrow space) d2.

[E] In a long-focal-length zooming range Zt from the second intermediatefocal length fm2 to the long focal length extremity ft, the firstsub-lens group S1 and the second sub-lens group S2 maintain the shorterdistance d2 therebetween, and the third sub-lens group S3 and the fourthsub-lens group S4 maintain the shorter distance d4 therebetween; and thefirst variable lens group 10 and the second variable lens group 20 movetowards the object side based on the positions thereof which aredetermined at the second intermediate focal length fm2, after the firstthrough fourth lens groups L1 through L4 have been moved towards theimage side, while changing the distance therebetween.

The zoom paths for the first variable lens group 10 and the secondvariable lens group 20 are simply depicted as straight lines in FIG. 6.It should be noted, however, that the actual zoom paths are notnecessarily straight lines.

Focusing is performed by integrally moving, in the optical axisdirection, the first sub-lens group S1 and the second sub-lens group S2,i.e., the first variable lens group 10 (first lens group frame 11)regardless of the zooming range.

Similar to the first through fifth embodiments, in the sixth embodiment,the zoom paths are discontinuous at the first intermediate focal lengthfm1 and the second intermediate focal length fm2; however, a solutionfor continuously forming a correct image plane exists by appropriatelydetermining the positions of the first sub-lens group S1 (first lensgroup L1), the second sub-lens group S2 (second lens group L2), thethird sub-lens group S3 (third lens group L3), and the fourth sub-lensgroup S4 (fourth lens group L4), respectively, at the short focal lengthextremity fw, the first and second intermediate focal lengths fm1, fm2(discontinuous line), and the long focal length extremity ft. Accordingto such a zoom path, a miniaturized zoom lens system having a high zoomratio can be obtained.

FIG. 7 shows the seventh embodiment of the zoom lens system with aswitching lens group. The zoom lens system includes a positive firstvariable lens group 10, and a negative second variable lens group 20, inthat order from the object side. The first variable lens group 10includes a positive first lens group L1 (first sub-lens group S1), anegative second lens group L2 (second sub-lens group S2) and a positivethird lens group L3 (third sub-lens group S3), in that order from theobject side. The second variable lens group 20 includes a negativefourth lens group L4. The first sub-lens group S1 and the third sub-lensgroup S3 are fixed to a first lens group frame 11. The second sub-lensgroup S2 is mounted on a movable sub-lens group frame 12. The movablesub-lens group frame 12 is arranged to move in the optical axisdirection, by a predetermined distance, along a guide groove 13 which isformed on the first lens group frame 11. The second sub-lens group S2 isselectively moved to either the object-side movement extremity at whichthe movable sub lens group frame 12 comes into contact with the frontend of the guide groove 13, or the image-side movement extremity atwhich the movable sub-lens group frame 12 comes into contact with therear end of the guide groove 13. The fourth lens group L4 of the secondvariable lens group 20 is fixed to a second lens group frame 21. Adiaphragm D is arranged to move together with the first variable lensgroup 10 (first lens group frame 11).

In the zoom paths according to the seventh embodiment, the firstvariable lens group 10 (first lens group frame 11), the second variablelens group 20 (second lens group frame 21), and the second sub-lensgroup S2 move in the following manner:

[A] In a short-focal-length zooming range Zw from the short focal lengthextremity fw to an intermediate focal length fm, the first sub-lensgroup S1 and the second sub-lens group S2 maintain a shorter distancetherebetween; however, the second sub-lens group S2 and the thirdsub-lens group S3 maintain a longer distance therebetween; and the firstvariable lens group 10 (first lens group frame 11) and the secondvariable lens group 20 (second lens group frame 21) move towards theobject side while changing the distance therebetween.

[B] At the intermediate focal length fm, the first variable lens group10 and the second variable lens group 20 are moved towards the imageside at the long focal-length extremity of the short-focal-lengthzooming range Zw; and the second sub-lens group S2 moves to theimage-side movement extremity of the guide groove 13, and wherein thesecond sub-lens group S2 moves away from the first sub-lens group S1 andmoves toward the third sub-lens group S3.

[C] In a long-focal-length zooming range Zt from the intermediate focallength fm to the long focal length extremity ft, the first sub-lensgroup S1 and the second sub-lens group S2 maintain the longer distancetherebetween, and the second sub-lens group S2 and the third sub-lensgroup S3 maintain the shorter distance therebetween; and the firstvariable lens group 10 and the second variable lens group 20 movetowards the object side based on the positions thereof which aredetermined at the intermediate focal length fm, after the first throughfourth lens groups L1 through L4 have been moving towards the imageside, while changing the distance therebetween.

The zoom paths for the first variable lens group 10 and the secondvariable lens group 20 are simply depicted as straight lines in FIG. 7.It should be noted, however, that the actual zoom paths are notnecessarily straight lines.

Focusing is performed by integrally moving, in the optical axisdirection, the first sub-lens group S1 through the third sub-lens groupS3, i.e., the first variable lens group 10 (first lens group frame 11)regardless of the zooming range.

Similar to the first through sixth embodiments, in the seventhembodiment, the zoom paths are discontinuous at the intermediate focallength fm; however, a solution for continuously forming a correct imageplane exists by appropriately determining the positions of the firstsub-lens group S1 (first lens group L1), the second sub-lens group S2(second lens group L2), the third sub-lens group S3 (third lens groupL3), and the fourth lens group L4, respectively, at the short focallength extremity fw, the intermediate focal length fm, (discontinuousline), and the long focal length extremity ft. According to such a zoompath, a miniaturized zoom lens system having a high zoom ratio can beobtained.

As can be understood from the above description, it is practical toapply the above-described zoom lens system having switching lens groupsto a photographing lens system of a camera in which the photographinglens system and a finder optical system are independently provided.Moreover, with respect to each of the first through fourth lens groupsL1 through L4, stopping positions at which the lens group stops uponzooming are preferably determined in a stepwise manner along afundamental zoom path, i.e., it is preferable to provide a plurality offocal-length steps. FIGS. 8 and 9 show zoom lens systems in whichpositions for stopping each lens group are determined in a stepwisemanner along the fundamental zoom paths. Since these zoom lens systemsare the same as that of the first embodiment, identical components areprovided with the same designators. The zoom paths are depicted withfundamental dotted lines; and positions at which the first lens groupframe 11 and the second lens group frame 21 stop are indicated withblack dots along the dotted lines. Further, in FIG. 9A, the dots areconnected by smooth (continuous) curved lines to form an actual zoompath. The actual mechanical structure thereof allows the first lensgroup frame 11 and the second lens group frame 21 to be moved along thesmooth curved lines (actual zoom path).

In the first through seventh embodiments, each lens group is illustratedas a single lens element; however, a lens group can of course include aplurality of lens elements.

FIGS. 9B and 9C depict an additional schematic view of the conceptsshown in FIGS. 8 and 9A. It should be noted in the following explanationthat FIGS. 9B and 9C are schematic in nature (e.g., not to scale and/ornot depicting actual shape) and that one skilled in the art willrecognize that the zoom paths are not necessarily straight, and themanner in which the schematics of FIGS. 9B and 9C relate to a designed(zooming) cam groove shape (which will differ depending at least on theoptical configuration). As shown in FIGS. 9B and 9C, if, in order toarrange movement in accordance with FIG. 9A, it is determined that onezoom path will be connected in an uninflected line (i.e., essentiallywithout discontinuity or inflection and without switching), then the camring, shape, and orientation of cam groove(s) can be adapted for thispurpose. As shown in FIG. 9B, each of the three fundamental zoom pathscan include a discontinuity. By smoothly connecting one zoom path, inthis case the second zoom path (e.g., depicted in the FIGS. 9B and 9C byshifting all of the zoom paths in the intermediate-to-telephoto range“up” so that the path of the second lens group is connected), it becomespossible to carry out the movements of the combined groups more simply.In this case, it is decided to use “switching” for the first group and asmooth inflection in the second group. As noted, the stepwisemovement/positioning and prohibition of photography in theswitching/inflection range also form part of this system.

Although FIG. 9C depicts a shift in which the second zoom path is madeessentially connected, the amount of shifting “up” does not need tofully align the curve to be made smoother, but need only take up aportion of the discontinuity (e.g., reducing any inflection to aselected amount, such as an imperceptible amount). In the followingdescription, it is noted that cam groove 44 f is essentially withoutdiscontinuity or inflection, relating to the second group zoom path inFIGS. 9A-9C, and that cam groove 44 r has a small inflection, relatingto the third group zoom path in FIGS. 9A-9C. However, the adaptationdepicted in FIGS. 9B and 9C can be used for any of the systems depictedin FIGS. 1-7 or variations thereof.

It can be decided to use at least one smooth or uninflected line forvarious reasons, including simplicity of movement, simplicity ofmanufacturing, or to improve exterior appearance of movement of lensbarrels (e.g., to avoid visible discontinuity in the operation of thelens barrels, so that an unsophisticated operator does not becomeconcerned about the proper operation of the camera). In the examplegiven, the movement of the lens barrel supporting the second lens groupis essentially continuous, while the switching movement of the firstlens group and the inflected movement of the third lens group cannot beseen from the exterior of the camera.

In each of the above-described embodiments, the first variable lensgroup 10 in FIGS. 1, 8, and 9A-9C, the second variable lens group 20 inFIG. 2, the second variable lens group 20 in FIG. 3, the first variablelens group 10 in FIG. 4, the first variable lens group 10 in FIG. 5, thefirst variable lens group 10 in FIG. 6, and the first variable lensgroup 10 in FIG. 7 (including the first lens L1 and the third lens L3 asa unit) are each switching lens groups which serve as focusing lensgroups in any focal length range.

A preferred embodiment will now be described in which the presentinvention has been applied to the zoom lens barrel in the examples shownin FIGS. 1, 8, and 9A-9C, which have a first variable lens group 10(switching lens group) and a second variable lens group 20.

FIGS. 10 through 31 show an embodiment of a zoom lens barrel (system).Unlike the zoom lens systems shown in FIGS. 1, 8 and 9, in which one ofthe first and second sub-lens groups S1 and S2, which together form aswitching lens group 10, is fixed to the first lens group frame 11, thefirst and second sub-lens groups S1 and S2 in this embodiment are bothmovable with respect to the switching lens group frame in the opticalaxis direction. In this embodiment, a moving path of the switching lensgroup frame upon zooming and a path of the first sub-lens group S1 andthe second sub-lens group S2 within the switching lens group frame canbe added to each other to give a composite zoom path, which correspondsto the zoom path shown in FIGS. 1, 8, and 9A-9C. Upon focusing, thefirst sub-lens group S1 and the second sub-lens group S2 are integrallymoved within the switching lens frame in the optical axis direction. Ina photographic operation, the first sub-lens group S1 and the secondsub-lens group S2 are placed at a predetermined position, before therelease of the shutter is started, as a result of the movement of theswitching lens group frame and the movement of the first sub-lens groupS1 and the second sub-lens group S2 within the switching lens groupframe in accordance with focal length information set by an operator(the photographer) and object distance information detected.

As shown in FIG. 10, a stationary barrel 42, which is fixed to a camerabody 41, has a female helicoid 43 formed on an inner surface of thestationary barrel 42. A male helicoid 45, which is formed on therearmost circumference of a cam ring 44, engages with the femalehelicoid 43. Arranged outside of the stationary barrel 42 is a pinion 47which is rotated by a zooming motor 46. Gear teeth (not shown) areformed on the circumference of the cam ring 44 wherein a part of themale helicoid 45 is cut out therefor. The gear teeth, which are formedto have the same oblique direction as the lead of the male helicoid 45,engages with the pinion 47. Accordingly, the cam ring 44 advances orretreats along the optical axis direction when the cam ring 44 isrotated in either direction by the zooming motor 46 due to theengagement of the female helicoid 43 and male helicoid 45. The positionof the cam ring 44 resulting from the rotation made by the zooming motor46 is detected by focal length detecting device 46C, which can include,for example, of a code plate and a brush.

A linear guide ring 48 is supported by the cam ring 44. The guide ring48 rotates relative to the cam ring 44 and moves together with the camring 44 along the optical axis direction (i.e., no relative displacementis allowed in the optical axis direction). The guide ring 48 issupported by a camera body 41 in a manner that enables the guide ring 48to move only in the optical axis direction. Arranged inside of the camring 44 in order from the front side of the cam ring 44 are a switchinglens group frame 50 (first lens group frame) which supports the firstvariable lens group 10 (i.e., the first sub-lens group S1 and secondsub-lens group S2) and a second lens group frame 49 which supports thesecond variable lens group 20. The switching lens group frame 50 and thesecond lens group frame 49 are linearly guided along the optical axisdirection by the guide ring 48.

Cam grooves 44 f and 44 r are formed on an inner surface of the cam ring44. The cam grooves 44 f and 44 r receive the switching lens group frame50 and second lens group frame 49, respectively. FIG. 11 shows anarrangement of the cam grooves 44 f and 44 r in a developed view. Threesets of the cam grooves 44 f and 44 r are formed circumferentially witheach groove spaced at equi-angular distances from one another. Radialfollower pins 50 p and 49 p are provided on the switching lens groupframe 50 and the second lens group frame 49 to be received in the camgrooves 44 f and 44 r, respectively.

The cam grooves 44 f and 44 r include introducing portions 44 f-a and 44r-a for the follower pins 50 p and 49 p, retracted portions 44 f-r and44 r-r for the zoom lens system, wide-angle extremity portions 44 f-wand 44 r-w, and telephoto extremity portions 44 f-t and 44 r-t,respectively. A rotational angle θ₁ is defined as the rotational anglefrom the introducing portions 44 f-a and 44 r-a to the retractedportions 44 f-r and 44 r-r, respectively. A rotational angle θ₂ isdefined as the rotational angle from the retracted portions 44 f-r and44 r-r to the wide-angle extremity portions 44 f-w and 44 r-w,respectively. A rotational angle θ₃ is defined as the rotational anglefrom the wide-angle extremity portions 44 f-w and 44 r-w to thetelephoto extremity portions 44 f-t and 44 r-t, respectively. Arotational angle θ₄, defined as the rotational angle beyond thetelephoto extremity portions 44 f-t and 44 r-t, which serves as arotational angle for assembly use. Each of the cam grooves 44 r for thesecond lens group frame 49 has an intermediate discontinuous position fmthat corresponds to the zoom path of the second variable lens group 20as described in the embodiments in FIGS. 1, 8 and 9.

In contrast, no discontinuous position appears to exist in the camgrooves 44 f for the first variable lens group 10 between the wide-angleextremity portion 44 f-w and the telephoto extremity portion 44 f-tsince the change in shape (profile) of each cam groove 44 f is smooth inthis area. This is because, in this embodiment, the switching lens groupframe 50 and the sub-lens group S2 are moved in such a manner that thepositions of the sub-lens group S2 are not discontinuous in theshort-focal-length zooming range Zw and in the long-focal-length zoomingrange Zt, the two ranges extending on both sides of intermediate focallength fm in FIG. 1. A connection line CC is schematically shown in FIG.1. The connection line CC connects the zoom path of theshort-focal-length zooming range Zw to zoom path of thelong-focal-length zooming range Zt, the two ranges extending on bothsides of the intermediate focal length fm. The cam groove 44 f is shapedto correspond to the zoom path connected by the connection line CC. Asthe follower pin 50 p moves along a section corresponding to theconnection line CC, the sub-lens group S1 moves from the object-sidemovement extremity to the image-side movement extremity. It is necessaryto control the zoom lens barrel so that the section of the cam groove 44f corresponding to the line CC is not used as an actual zooming range ina photographic operation (i.e., the cam ring 44 is not stopped).Alternatively, the cam grove 44 f can include the discontinuous positionsimilar to that of the cam groove 44 r.

In the above-described zoom lens barrel, the cam ring 44 advances orretreats along the optical axis while rotating as the pinion 47 isrotated via the zooming motor 46 in either direction, which causes theswitching lens group frame 50 (i.e., the first variable lens group 10)and the second lens group frame 49 (i.e., the second variable lens group20), which are guided in the optical axis direction within the cam ring44, to move in the optical axis direction along a predetermined pathdefined by the cam grooves 44 f and 44 r.

Novel features of the present embodiment reside in a support structureby which the first sub-lens group S1 and the second sub-lens group S2are supported in the switching lens group frame 50 and the drivingstructure thereof. A particular example of an arrangement within theswitching lens group frame 50 will now be described by reference toFIGS. 12 through 31.

As shown in FIGS. 15 and 16, a front shutter retaining ring 51, a rearshutter retaining ring 52, a first sub-lens group frame 53, a secondsub-lens group frame 54, an actuator ring 55, and a gear holding ring 56are arranged within the switching lens group frame 50. The front shutterretaining ring 51, the rear shutter retaining ring 52, and the gearholding ring 56 form a portion of the switching lens group frame 50. Thefirst sub-lens group S1 is fixed to the first sub-lens group frame 53,and the second sub-lens group S2 is fixed to the second sub-lens groupframe 54. The first sub-lens group frame 53, the second sub-lens groupframe 54, and the actuator ring 55 are movably fitted in a centralopening 51 p (see FIG. 12) of the front shutter retaining ring 51. Thesemovable members, i.e., the first sub-lens group frame 53, the secondsub-lens group frame 54, and the actuator ring 55, enable the firstsub-lens group S1 and the second sub-lens group S2 to be at a mutuallyclose position, or be at a mutually distant position, with respect tothe optical axis direction, and also enable the first sub-lens group S1and the second sub-lens group S2 to perform focusing.

The actuator ring 55 is rotatably supported between the front and rearshutter retaining rings 51 and 52 with the rearmost portion of theactuator ring 55 being restricted by a receiving surface 52 a (FIGS. 13,15, and 16) of the rear shutter retaining ring 52. The actuator ring 55is a driving member that enables the first sub-lens group S1 and thesecond sub-lens group S2 to become mutually close or mutually distantfrom each other, and enables the first and the second sub-lens groups S1and S2 to perform focusing via the rotation thereof. The gear holdingring 56 is fixed to the front end of the front shutter retaining ring51, and a lens shutter mechanism 57 and a diaphragm mechanism 58 aresupported by the rear shutter retaining ring 52 (FIGS. 12, 15, and 16).

The first sub-lens group frame 53 has a cylindrical shape and has twolinear guide ribs 53 a on its periphery at the opposite sides thereof atan equi-angular interval of 180 degrees. A guide bore 53 b is formed inthe guide rib 53 a. A guide rod 59 is loosely inserted (or moveablyfitted) in the guide bore 53 b. The rear end of the guide rod 59 isfixed in a fixing bore 56 q formed at the rearmost portion of the gearholding ring 56 while the front end of the guide rod 59 is fixed to thefront surface of the gear holding ring 56 by a bracket 60 and a screw61. A coil spring 62 is placed over each of the guide rod 59 between thebracket 60 and the guide rib 53 a so that the coil spring 62 biases thefirst sub-lens group frame 53 toward the second sub-lens group frame 54.A U-shaped recess 56 r is provided on the gear holding ring 56 so as toreceive the guide rod 59 and the spring 62 (FIGS. 25 through 27). Therecess 56 r communicatively connects with the central opening 51 p ofthe front shutter retaining ring 51. The first sub-lens group frame 53can be connected to the front shutter retaining ring 51 by engaging theguide ribs 53 a with the guide rods 59 of the front shutter retainingring 51 at two positions, wherein the guide ribs 53 a are provided onthe first sub-lens group frame 53 at 180° intervals about the opticalaxis.

As shown in FIGS. 17A, 18A, 19A and 20A, the first sub-lens group frame53 is provided with four shift leading surfaces (shift cam surfaces) 53c that are formed circumferentially at equi-angular intervals on theend-face of the first sub-lens group frame 53. Annular light-blockingsupport ribs 53 d (see FIG. 14) are provided radially outside of theshift leading surfaces 53 c over the open ends of the shift leadingsurfaces 53 c. FIG. 23 shows an enlarged expanded view of one of theshift leading surfaces 53 c which is formed essentially as a straightslope having an inclination angle α with respect to a circumferentialedge of the first sub-lens group 53 (i.e., with respect to a planenormal to the optical axis), and is provided with a pair of followerengaging recesses 53 e and 53 f on either end of the shift leadingsurface 53 c. Each of the engaging recesses 53 e and 53 f is formed as ashallow V-shaped recess. The follower engaging recess 53 e defines amutually distant position on the wide-angle side and the followerengaging recess 53 f defines a mutually close position on the telephotoside, of the first sub-lens group frame 53 and the second sub-lens groupframe 54 (i.e., the first sub-lens group S1 and second sub-lens groupS2).

As shown in FIGS. 17A, 18A, 19A and 20A, the second sub-lens group frame54 is provided on its periphery with four follower projections 54 a,each corresponding to each of the four shift leading surfaces 53 c ofthe first sub-lens group frame 53. An inclined surface 54 b is providedso as to correspond to the shift leading surface 53 c of the firstsub-lens group frame 53, and the follower projection 54 a is provided onthe end of the inclined surface 54 b which is the closest to the shiftleading surface 53 c. The tip of the follower projection 54 a has asubstantially semi-circular shape which is symmetrical with respect tothe longitudinal axis thereof, so that the shapes of the engagingrecesses 53 e and 53 f correspond to the tip shape of the projection 54a. Annular light-blocking support ribs 54 c are radially provided on thesecond sub-lens group frame 54 inside the projections 54 a and theinclined surfaces 54 b. The shift leading surfaces 53 c formed on thefirst sub-lens group frame 53 and the follower projections 54 a formedon the second sub-lens group frame 54 together form a shift cammechanism (of a lens group (lens frame) shift mechanism) that enablesthe lens-group frames 53 and 54 either be at a mutually close position,or be at a mutually distant position. As described above, the four shiftleading surfaces 53 c of the first sub-lens group frame 53 and the fourprojections 54 a of the second sub-lens group frame 54 are spaced atequi-angular intervals. Accordingly, each of the surfaces can engagewith its respective projection at 180° intervals of a relative rotation.Given that N is the number of the shift leading surfaces 53 c or thefollower projections 54 a (four, in this embodiment) and that M is thenumber of the guide ribs 53 a of the first sub-lens group frame 53 orthe number of the guide rods 59 of the front shutter retaining ring 51(two, in this embodiment), the relationship between M and N is that M isa multiple of N, or in other words, N is a divisor of M. Thisrelationship makes it possible to select an assembly position from amongdifferent assembly positions, so that for example, an assembly positionthat provides optimum optical performance can be achieved.

Furthermore, a pair of linear guide projections 54 d are formed on thesecond sub-lens group frame 54 on the outer surface thereof. The guideprojections 54 d are formed at the same circumferential positions as twoof the four follower projections 54 a that are positioned on theperiphery of the second sub-lens group frame 54 at the opposite sidesthereof at an equi-angular interval of 180 degrees. Each of the guideprojections 54 d is formed at a position which is rearward with respectto the follower projection 54 a in the optical axis direction. Alsoformed on the second sub-lens group frame 54 on the outer surfacethereof are three lugs 54 e, which are spaced at equi-angular intervals,and are positioned rearward with respect to the guide projection 54 d inthe optical axis direction. As best shown in FIG. 24, each lug 54 e hasa pair of contact surfaces N1 and N2 that are spaced apart from eachother in a circumferential direction. Each lug 54 e also has a smoothcircular shaped end surface N3 that is symmetrical with respect to thecentral axis of the lug 54 e extending in the middle of the contactsurfaces N1 and N2.

As shown in FIG. 24, a pair of rotation preventing surfaces 51 a and 51b are formed on the front shutter retaining ring 51 on the inner surfacethereof, in order to define the range of rotation of the second sub-lensgroup frame 54 relative to the non-rotating front shutter retaining ring51, with respect to the guide projection 54 d of the second sub-lensgroup frame 54. The rotation preventing surfaces 51 a and 51 b come intocontact with contact surfaces M1 and M2 of the guide projection 54 d,respectively, when the second sub-lens group frame 54 is rotated ineither direction, thereby defining the rotational movement extremitiesof the second sub-lens group frame 54. A wide-angle linear guide slot 51d is defined between the rotation preventing surface 51 a and a guidesurface 51 c which comes into contact with the contact surface M2 of theguide projection 54 d. A telephoto linear guide slot 51 f is definedbetween the rotation preventing surface 51 b and a guide surface 51 ewhich comes into contact with the contact surface M1 of the guideprojection 54 d. Thus, the width of both of the wide-angle linear guideslot 51 d and the telephoto linear guide slot 51 f in thecircumferential direction corresponds to that of the linear guideprojection 54 d in the same direction. Accordingly, the guide projection54 d snugly fit in the guide slots 51 d and 51 f so as to movabletherein.

The clearance between the wide-angle linear guide slot 51 d or thetelephoto linear guide slot 51 f and the guide projection 54 d isdetermined smaller (stricter) than the clearance between the guide bore53 b of the first sub-lens group frame 53 and the guide rod 59. Thelinear guide projections 54 d are provided on the periphery of thesecond sub-lens group frame 54 on opposite sides thereof at anequi-angular interval of 180 degrees. A pair of the wide-angle andtelephoto linear guide slots 51 d and 51 f are provided on the frontshutter retaining ring 51 so that two linear guide projections 54 d canbe selectively received in the wide-angle and telephoto linear guideslots 51 d and 51 f with respect to the rotational positions thereof(i.e., at an angular interval of 180 degrees).

The actuator ring 55 has, on the front end surface thereof, threecontrol recesses 55 a that each correspond to each of the lugs 54 e ofthe second sub-lens group frame 54 (see FIG. 22). Each of the controlrecesses 55 a has a shape that is symmetrical with respect to thecentral axis extending parallel to the optical axis and includes a pairof effective surfaces 55 b and 55 c that respectively come into contactwith contact surfaces N1 and N2. The lugs 54 e of the second sub-lensgroup frame 54 and the control recesses 55 a constitute a focusing cammechanism of a focusing mechanism. The control recess 55 a also includesa pair of focus leading surfaces 55 d and 55 e (focus cam surfaces) onthe telephoto side and on the wide-angle side, respectively. The focusleading surfaces 55 d and 55 e each come into contact with the circularend surface N3 of the lug 54 e. The telephoto-side focus leading surface55 d and the wide-angle-side focus leading surface 55 e are providedbetween the effective surfaces 55 b and 55 c in the form of an end-facedcam having an open front end. The slopes of the leading surfaces 55 dand 55 e have opposite directions with respect to the circumferentialdirection thereof, but have the same absolute value, i.e., the slopesboth incline forwards in the optical axis direction. Annularlight-blocking support ribs 55 f (see FIG. 13) are provided radiallyoutside, and over the front portion, of the control recess 55 a of theactuator ring 55. The focus leading surfaces 55 d and 55 e, togetherwith the lug 54 e provided on the second sub-lens group frame 54, form afocus cam mechanism. As described above, the three lugs 54 e of thesecond sub-lens group frame 54 and the three control recesses 55 a ofthe actuator ring 55 are spaced at equi-angular intervals. In theillustrated embodiment, each of the lugs can engage with a respectiverecess at 120° angular intervals.

The aforementioned coil springs 62, which bias the first sub-lens groupframe 53 rearward, so that the shift leading surfaces 53 c contact thefollower projections 54 a, and the lugs 54 e of the second sub-lensgroup frame 54 contact the telephoto side or wide-angle side focusleading surfaces 55 d or 55 e of the actuator ring 55. As describedabove, the rear end surface of the actuator ring 55 abuts the receivingsurface 52 a of the rear shutter retaining ring 52. Accordingly, thefirst sub-lens group frame 53, the second sub-lens group frame 54, theactuator ring 55, and the rear shutter retaining ring 52 (receivingsurface 52 a) can be held in contact by the sole force exerted by thecoil springs 62. As can be clearly seen from FIGS. 15 and 16, when thefirst sub-lens group frame 53, the second sub-lens group frame 54, theactuator ring 55, and the rear shutter retaining ring 52 are inengagement with each other, the front end of the second sub-lens groupframe 54 is positioned inside the first sub-lens group frame 53, and theactuator ring 55 is situated on the periphery of the second sub-lensgroup frame 54.

FIG. 21(A through H) shows the manner in which the first sub-lens groupframe 53 and the second sub-lens group frame 54 (i.e., the firstsub-lens group S1 and the second sub-lens group S2) are moved via theeffective surfaces 55 b and 55 c between a mutually close position onthe telephoto side and a mutually distant position on the wide-angleside. Note that, solid line arrows represent the rotational direction ofthe actuator ring 55, in FIG. 21.

The arrangement shown in FIG. 21(A) is the mutually distant position onthe wide-angle side, in which the effective surface 55 b of the actuatorring 55 abuts the lug 54 e, and the linear guide projection 54 d of thesecond sub-lens group frame 54 is disengaged from the wide-angle linearguide slot 51 d. As the actuator ring 55 rotates in a clockwisedirection (i.e., moves to the right in FIG. 21), the effective surface55 b biases the contact surface N1 of the lug 54 e to rotate the secondsub-lens group frame 54 clockwise (to the right in FIG. 21) until thelinear guide projection 54 d abuts the rotation preventing surface 51 b(FIGS. 21(A) through 21(C)). During the rotation of the actuator ring 55and the second sub-lens group frame 54, the first sub-lens group frame53 (i.e., the first sub-lens group S1) follows the shift leading surface53 c, and the follower projection 54 a of the second sub-lens groupframe 54 so that the first sub-lens group frame 53 linearly moves closerto the second sub-lens group frame 54 (i.e., the second sub-lens groupS1) (FIG. 21(B)). Ultimately, the follower projection 54 a engages withthe follower engaging recess 53 f and rearward movement of the firstsub-lens group frame 53 with respect to the second sub-lens group frame54 in the optical axis direction is stopped (FIG. 21(C)). Since thefollower projections 54 a and the follower engaging recesses 53 f arespaced at equi-angular intervals therebetween, eccentricity between thefirst sub-lens group frame 53 and the second sub-lens group frame 54 isprevented, with all of the projections and the recesses in engagement.This completes the switching from the mutually distant position on thewide-angle side to the mutually close position on the telephoto side,resulting in the first sub-lens group S1 being in a mutually closeposition with respect to the second sub-lens group S2 (i.e., mutuallyclose extremity). Note that the actuator ring 55 cannot rotate furtherin this direction.

Upon completion of switching to the mutually close position on thetelephoto side, the rotation of the actuator ring 55 is reversed. Thelug 54 e (i.e., the second sub-lens group frame 54) moves rearwardfollowing the telephoto side focus leading surface 55 d until the linearguide projection 54 d engages with the telephoto linear guide slot 51 f.This allows the linear projection 54 d to move only in the optical axisdirection (FIG. 21(D)). Focusing is carried out on the telephoto sidefrom the intermediate focal length to the long focal length extremity,with the second sub-lens group frame 54 and the first sub-lens group 53being moved integrally at the mutually close position via the telephotoside-focus leading surface 55 d.

Once the actuator ring 55 is rotated until the effective surface 55 cabuts the contact surface N2 of the lug 54 e, the linear guideprojection 54 d of the second sub-lens group frame 54 disengages fromthe telephoto linear guide slot 51 f (FIG. 21(E)).

At this point, the rotation of the actuator ring 55 has been reversed(upon or after completion of the switching to the mutually closeposition on the telephoto side). As the actuator ring 55 rotatescounterclockwise (i.e., moves to the left in FIG. 21), the effectivesurface 55 c biases the contact surface N2 of the lug 54 e to rotate thesecond sub-lens group frame 54 leftward until the contact surface M1 ofthe linear guide projection 54 d abuts the rotation preventing surface51 a (FIGS. 21(F) and 21(G)). During the rotation of the actuator ring55 and the second sub-lens group frame 54, the first sub-lens groupframe 53 follows the shift leading surface 53 c and the followerprojection 54 a of the second sub-lens group frame 54 so that the firstsub-lens group frame 53 linearly moves away from the second sub-lensgroup frame 54. Ultimately, the follower projection 54 a engages withthe follower engaging recess 53 e and forward movement of the firstsub-lens group frame 53 with respect to the second sub-lens group frame54 in the optical axis direction is stopped (FIG. 21(G)). Since thefollower projections 54 a and the follower engaging recesses 53 f arespaced at equi-angular intervals therebetween, eccentricity between thefirst sub-lens group frame 53 and the second sub-lens group frame 54 isprevented, with all of the projections and the recesses in engagement.This completes the switching from the mutually close position on thetelephoto side to the mutually distant position on the wide-angle side,resulting in the first sub-lens group S1 being in a mutually distantposition with respect to the second sub-lens group S2 (i.e., mutuallydistant extremity). Note that the actuator ring 55 cannot rotate furtherin this direction.

Upon completion of switching to the mutually distant position on thewide-angle side, the rotation of the actuator ring 55 is reversed. Thelug 54 e (i.e., the second sub-lens group frame 54) moves rearwardfollowing the wide-angle side focus leading surface 55 e until thelinear guide projection 54 d engages with the wide-angle linear guideslot 51 d. This allows the linear projection 54 d to move only along thedirection of the optical axis (FIGS. 21(G) and 21(H)). Focusing iscarried out on the wide-angle side from the intermediate focal length tothe short focal length extremity, with the second sub-lens group frame54 and the first sub-lens group frame 53 being moved integrally at themutually distant extremity via the wide-angle side focus leading surface55 e.

Once the actuator ring 55 is rotated until the effective surface 55 cabuts the contact surface N1 of the lug 54 e, the linear guideprojection 54 d of the second sub-lens group frame 54 disengages fromthe wide-angle linear guide slot 51 d, and the positions of the firstsub-lens group frame 53 and the second sub-lens group frame 54 returnback to the position shown at FIG. 21(A).

FIG. 22 shows the principle of how the focusing is carried out via thetelephoto side-focus leading surface 55 d and the wide-angle side-focusleading surface 55 e. As the actuator ring 55 is rotated in a telephotoside focusing range pt (from an infinite photographic distance ∞ to aminimum photographic distance (object at a minimum distance) n), withthe circular end surface N3 of the lug 54 e in contact with thetelephoto side focus leading surface 55 d, the second sub-lens groupframe 54 (whose rotation is confined by the linear guide projection 54 dwhich is in engagement with the telephoto linear guide slot 51 f) andthe first sub-lens group frame 53 (i.e., the first sub-lens group S1 andthe second sub-lens group S2) integrally moves forwardly or rearwardlyalong the optical axis to thereby carry out focusing. Similarly, as theactuator ring 55 is rotated in a wide-angle side focusing range pw (froman infinite photographic distance ∞ to a minimum photographic distance(object at a minimum distance) n), with the circular end surface N3 ofthe lug 54 e in contact with the wide-angle side focus leading surface55 e, the second sub-lens group frame 54 (whose rotation is confined bythe linear guide projection 54 d which is in engagement with thewide-angle linear guide slot 51 d) and the first sub-lens group frame 53(i.e., the first sub-lens group S1 and the second sub-lens group S2)integrally moves forwardly or rearwardly along the optical axis toprovide focusing.

In particular, focusing on the telephoto side and focusing on thewide-angle side are achieved by controlling the number of pulses countedby a encoder 64 p (see FIG. 30) provided in a driving system whichdrives the actuator ring with respect to a reference position at whichthe linear guide projection 54 d of the second sub-lens group frame 54comes into contact with the rotation preventing surface 51 a or 51 b(i.e., the position where the rotation of the actuator ring 55 isreversed). For example, the number of pulses of the driving systemrequired to move the focusing lens groups (i.e., the sub-lens groups S1and S2) from a reference position to a position corresponding to aminimum photographic distance n, to a position corresponding to aninfinite photographic distance ∞, and to a position corresponding to anintermediate photographic distance can be predetermined by taking theleading angles for the focus leading surfaces 55 d and 55 e intoconsideration. Accordingly, focusing can be properly carried out inaccordance with the object distance information by managing the numberof the pulses of the encoder.

Also, in the illustrated embodiment, the slopes of the telephoto sidefocus leading surface 55 d and the wide-angle side focus leading surface55 e of the actuator ring 55 have opposite directions with respect tothe circumferential direction thereof, but have the same absolute value,i.e., the slopes both incline forwards in the optical axis direction,and the lug 54 e is shaped to be symmetrical with respect to the centralaxis extending in the middle of the contact surfaces N1 and N2 which arecircumferentially spaced apart from each other. Accordingly, focusingcan be carried out on the telephoto side in the same manner as on thewide-angle side. This facilitates focusing control.

FIGS. 17A and 17B show an arrangement of the first sub-lens group frame53, the second sub-lens group frame 54, the actuator ring 55, and thefront shutter retaining ring 51 when the first sub-lens group frame 53(i.e., the first sub-lens group S1) and the second sub-lens group frame54 (i.e., the second sub-lens group S2) are in the mutually distantposition at the wide-angle side, and are in a position so as to focus onan object at infinity. FIGS. 18A and 18B show an arrangement of thefirst sub-lens group frame 53, the second sub-lens group frame 54, theactuator ring 55, and the front shutter retaining ring 51 when the firstsub-lens group frame 53 and the second sub-lens group frame 54 are inthe mutually distant position on the wide-angle side, and are in aposition so as to focus on an object at a minimum distance. FIGS. 19Aand 19B show an arrangement of the first sub-lens group frame 53, thesecond sub-lens group frame 54, the actuator ring 55, and the frontshutter retaining ring 51 when the first sub-lens group frame 53 and thesecond sub-lens group frame 54 are in the mutually close position on thetelephoto side, and are in a position so as to focus on an object atinfinity. FIGS. 20A and 20B show an arrangement of the first sub-lensgroup frame 53, the second sub-lens group frame 54, the actuator ring55, and the front shutter retaining ring 51 when the first sub-lensgroup frame 53 and the second sub-lens group frame 54 are in themutually close position on the telephoto side, and are in a position soas to focus on an object at a minimum distance. The first sub-lens groupframe 53, the second sub-lens group frame 54, the actuator ring 55, andthe front shutter retaining ring 51 are shown separated in the opticalaxis direction in FIGS. 17A, 18A, 19A and 20A, and are shown inoperation in FIGS. 17B, 18B, 19B and 20B.

Gear teeth 55 g are formed over a circumference on the rear-endperiphery of the actuator ring 55. As shown in FIGS. 12, 29 and 30, thegear teeth 55 g engage with a series of reduction gears 63 a. The seriesof reduction gears 63 a are rotated in either direction by abi-directional motor 64 which also includes the encoder 64 p. The seriesof reduction gears 63 a are held between the front shutter retainingring 51 and the gear holding ring 56, and the bi-directional motor 64 isheld by the rear shutter retaining ring 52. The gear teeth 55 g of theactuator ring 55, which are formed over the entire periphery thereof,makes it easy for the three control recesses 55 a to engage with thethree lugs 54 e of the second sub-lens group frame 54 at differentrelative rotational positions that are separated by 120°.

The lens shutter mechanism 57 and the diaphragm mechanism 58 are mountedon the rear shutter retaining ring 52. In particular, as shown in FIGS.12, 15 and 16, the lens shutter mechanism 57 includes a shutter sectorsupport plate 57 a, three shutter sectors 57 b, and a shutter drive ring57 c for opening and closing the shutter sectors 57 b. The diaphragmmechanism 58 includes a diaphragm sector support plate 58 a, threediaphragm sectors 58 b, and a diaphragm drive ring 58 c for opening andclosing the diaphragm sectors 58 b. These components are retained in therear shutter retaining ring 52 by a sector holding ring 57 d. Theshutter sector 57 b and the diaphragm sector 58 b include a pair ofdowels. One of the dowels is rotatably supported by the support plates57 a and 58 a and the other is rotatably fitted to the drive rings 57 cand 58 c. The lens shutter mechanism 57 opens and closes an apertureformed by the shutter sectors 57 b as the shutter drive ring 57 c isrotated. The diaphragm mechanism 58 varies the size of an apertureformed by the diaphragm sectors 58 b as the diaphragm drive ring 58 c isrotated.

Sector gear teeth 57 g are formed on a part of the periphery of theshutter drive ring 57 c and engage with a series of reduction gears 63 bthat are sequentially arranged from a shutter drive motor 57 m (see FIG.12). When the shutter drive motor 57 m is rotated in either direction,the aperture, which has been closed by the shutter sectors 57 b, ismomentarily opened and is then closed again. In the zoom lens barrel ofthe illustrated embodiment, the shutter sectors 57 b serve both as avariable diaphragm to provide an aperture of an arbitrary size, and as ashutter. The shutter sectors 57 b are electrically controlled so thatthe size of the aperture of the shutter sectors 57 b (aperture value)and the length of time during which the aperture is left opened (i.e.,shutter speed) can be varied depending on the exposure, upon the releaseof the shutter. Furthermore, the diaphragm drive ring 58 c includes alug 58 g on the periphery thereof. The lug 58 g engages with adiaphragm-controlling cam slot 48 s formed on an inner surface of thelinear guide ring 48 (see FIG. 10). Upon zooming, the linear guide ring48 and the rear shutter retaining ring 52 (i.e., the diaphragm drivering 58 c) moves relative to each another in the optical axis direction.This causes the lug 58 g to follow the diaphragm-controlling cam slot 48s so as to move in the circumferential direction. This in turn causesthe diaphragm drive ring 58 c to rotate and, as a result, the size ofthe aperture formed by the diaphragm sectors 58 b is varied. Thediaphragm sector 58 b is provided to restrict the maximum value of theaperture diameter especially in the wide-angle side photographing range,and the degree of opening of the aperture is mechanically varied inaccordance with the amount of extension of the zoom lens barrel.

As shown in FIG. 31, the zooming motor 46 for the cam ring 44, thebi-directional motor 64 for the actuator ring 55, and the shutter drivemotor 57 m for the lens shutter mechanism 57 are controlled by a controlcircuit (control device) 66. Focal length information 67, which is setby the user (photographer) via a zoom switch or the like, detectedobject distance information 68, object brightness information 69,information on rotational positions of the cam ring 44, which isprovided by a focal length detecting device 46C, and information onrotational positions of the motor 64, which is provided by the encoder64 p, are inputted to the control circuit 66. The zooming motor 46, thebi-directional motor 64 and the shutter drive motor 57 m are controlledaccording to the inputted information so that exposure is carried outunder proper exposure conditions in accordance with the predeterminedfocal lengths. While the shutter sectors 57 b serve both as a shutterand as a variable diaphragm, and the diaphragm sectors 58 b restrict theaperture diameter upon photographing on the wide-angle side in thisembodiment, the diaphragm sectors 58 b can be provided as a motor-drivenvariable diaphragm mechanism.

In the illustrated embodiment, the focal length detecting device 46C(i.e., a rotational position detecting device for the cam ring 44)detects rotational positions of the cam groove 44 f which correspond tothe connection line CC (see FIG. 1), such that the control circuit 66does not allow the cam ring 44 to stop in this section. If the zoom lenssystem is provided as a step zoom lens, positions at which the cam ring44 stops are controlled in a stepwise manner. As described above, whilethe operations, corresponding to the preset focal length, distance tothe object, and the brightness of the object, of the zoom lens barrel(i.e., photographing optical system) having the above-describedswitching lens group can be completed immediately before the shutter isreleased, the focal length set by an operator can be confirmed via aseparate finder optical system (not shown) that is provided separatefrom the photographing optical system.

In the zoom lens barrel using the lens barrel for the switching lensgroups, positions at which the switching lens group frame 50, the firstsub-lens group frame 53, and the second sub-lens group frame 54 stopupon a photographic operation can be practically determined in astepwise manner along the zoom path.

Note that, while the lens support/drive structure has been describedwith regard to the first variable lens group 10 shown in FIGS. 1, 8 and9, the mechanical construction of the above-described lens barrel isalso applicable to the second variable lens group 20 in FIG. 2, thesecond variable lens group 20 in FIG. 3, the first variable lens group10 in FIG. 4, the first variable lens group 10 in FIG. 5, the firstvariable lens group 10 in FIG. 6, and the first variable lens group 10in FIG. 7 (the first lens L1 is integrally formed with the third lensL3).

In the above-described lens barrel, the first sub-lens group (frontsub-lens group) S1 and the second sub-lens group (rear sub-lens group)S2, which together form the switching lens group 10, are supported inthe first sub-lens group frame (front lens group frame) 53 and thesecond sub-lens group frame (rear lens group frame) 54, respectively.The four shift leading surfaces (shift cam surfaces) 53 c, provided onthe rear end of the first sub-lens group frame 53, cooperate with thefour follower projections 54 a, provided on the front end of the secondsub-lens group frame 54, to move the first sub-lens group frame 53 andthe second sub-lens group frame 54 toward each other until they reachthe mutually close position on the telephoto side, and move the firstsub-lens group frame 53 and the second sub-lens group frame 54 away fromeach other until they reach the mutually distant position on thewide-angle side. When the first and the second sub-lens group frames 53and 54 are in the mutually close position or in the mutually distantposition, the follower projections 54 a engage either with the followerengaging recesses 53 e or the follower engaging recesses 53 f. Thefollower engaging recesses 53 e and 53 f are formed at the opposite endsof the shift leading surfaces 53 c. Namely, the first sub-lens groupframe 53 and the second sub-lens group frame 54 are kept engaged whilebeing able to slide relative to one another. The relative positions ofthe sub-lens group frames 53 and 54 in the axial direction (i.e., thedistances between the sub-group frames 53 and 54) when in the mutuallyclose position on the telephoto side or in the mutually distant positionon the wide-angle side are determined by the construction that providesthe engagement between the sub-lens group frames 53 and 54.

As shown in FIGS. 10, 15 and 16, a first sub-lens group contact surface(first lens group positioning surface) 53 m is provided substantiallyhalf-way in the first sub-lens group frame 53 in the axial direction(the direction parallel to the optical axis of the first sub-lens groupS1). The first sub-lens group contact surface 53 m is formed as anannular surface facing the front end opening of the first sub-lens groupframe 53. The outer diameter of the first sub-lens group contact surface53 m corresponds to the diameter of the first sub-lens group S1, and theinner diameter thereof is smaller than the outer diameter of the rearsurface of the first sub-lens group S1. The first sub-lens group contactsurface 53 m is formed so as to stably receive the rear end surface ofthe fist sub-lens group S1. A cylindrical portion of the first sub-lensgroup frame 53 provided in front of the first sub-lens group contactsurface 53 m has an inner diameter as large as the largest diameter ofthe first sub-lens group frame contact surface 53 m. This allows thefirst sub-lens group S1 to be inserted in a rearward direction (i.e.,toward the first sub-lens group contact surface 53 m) through the frontend opening of the first sub-lens group frame 53 without causing anyinterference between the first sub-lens group S1 and the first sub-lensgroup frame 53.

When the lens barrel is assembled, the first sub-lens group S1 isinserted into the first sub-lens group frame 53 from the front endopening of the first sub-lens group frame 53. The first sub-lens groupS1 is inserted into the first sub-lens group frame 53 by a predeterminedamount from the front end opening until a portion of the rear surface ofthe first sub-lens group S1 comes into contact with the first sub-lensgroup contact surface 53 m, and further insertion of the first sub-lensgroup S1 is prevented. At this stage, the area around the front end ofthe first sub-lens group frame 53 is heat-sealed to prevent the firstsub-lens group S1 from coming out and holds the first sub-lens group S1in place within the first sub-lens group frame 53. The heat-sealed areaof the first sub-lens group frame 53 is denoted by a reference numeral53 n in FIGS. 10, 15 and 16.

As shown in FIGS. 10, 15 and 16, a second sub-lens group contact surface(second lens group positioning surface) 54 m is provided on the secondsub-lens group frame 54 in the vicinity of the front end thereof asviewed in the axial direction (i.e., the direction parallel to theoptical axis of the second sub-lens group S2). In contrast to the firstsub-lens group contact surface 53 m of the first sub-lens group frame53, the second sub-lens group contact surface 54 m is an annular surfacefacing the rear end opening of the second sub-lens group frame 54. Theinner diameter of the second sub-lens group contact surface 54 m issmaller than the outer diameter of the front end of the second sub-lensgroup S2. The second sub-lens group contact surface 54 m is formed so asto stably receive the front surface of the second sub-lens group S2. Acylindrical portion of the second sub-lens group frame 54 to the rear ofthe second sub-lens group contact surface 54 m has an inner diameterthat is equal to, or larger than, the largest diameter of the secondsub-lens group frame contact surface 54 m. This allows the secondsub-lens group S2 to be inserted in a frontward direction (i.e., towardthe second sub-lens group contact surface 54 m) through the rear endopening of the second sub-lens group frame 54 without causing anyinterference between the second sub-lens group S2 and the secondsub-lens group frame 54.

When the lens barrel is assembled, the second sub-lens group S2 isinserted into the second sub-lens group frame 54 from the rear endopening of the second sub-lens group frame 54. The second sub-lens groupS2 is inserted into the second sub-lens group frame 54 by apredetermined amount from the rear end opening until a portion of thefront surface of the second sub-lens group S2 comes into contact withthe second sub-lens group contact surface 54 m, and further insertion ofthe second sub-lens group S2 is prevented. At this stage, the areaaround the rear end of the second sub-lens group frame 54 is heat-sealedto prevent the second sub-lens group S2 from coming out and holds thesecond sub-lens group S2 in place within the second sub-lens group frame54. The heat-sealed area of the second sub-lens group frame 54 isdenoted by a reference numeral 54 n in FIGS. 10, 15 and 16.

As can be clearly seen in FIGS. 10, 15 and 16, the first sub-lens groupcontact surface 53 m, which determines the position of the firstsub-lens group S1 in the optical axis direction with respect to thefirst sub-lens group frame 53, specifically serves as a positioningsurface to define the rearmost position of the first sub-lens group S1.Similarly, the second sub-lens group contact surface 54 m, whichdetermines the position of the second sub-lens group S2 in the opticalaxis direction with respect to the second sub-lens group frame 54,specifically serves as a positioning surface to define the frontposition of the second sub-lens group S2. In other words, the lens grouppositioning surfaces are provided such that the rear surface of thefirst sub-lens group S and the front surface of the second sub-lensgroup S2, which oppose each another, are positioned in the firstsub-lens group frame 53 and in the second sub-lens group frame 54,respectively. Accordingly, the distances V1 and V2 (see FIGS. 15 and 16)between the first sub-lens group S1 and the second sub-lens group S2when in the mutually distant position on the wide-angle side and in themutually close position on the telephoto side are stabilized.

If, unlike the invention, the second sub-lens group S2 were to beinserted rearward and the rear surface of the second sub-lens group S2abuts a positioning surface provided on the sub-lens group frame, theaccuracy in positioning the front surface of the second sub-lens groupS2 becomes susceptible to the accumulation of tolerances in lensthickness, making it difficult to stabilize the distances V1 and V2between the first sub-lens group S1 and the second sub-lens group S2without providing an adjustment mechanism.

Also, as shown in FIGS. 10, 15 and 16, the rear end portion of the firstsub-lens group frame 53 and the front end portion of the second sub-lensgroup frame 54 overlap each other. These portions slide with respect toone another when the first sub-lens group frame 53 and the secondsub-lens group frame 54 move to assume the mutually close position andthe mutually distant position. Smooth sliding of these sliding portionsmay be interrupted when they include a sealed region. In the presentembodiment, however, the first sub-lens group frame 53 includes a sealedregion in the front end portion thereof and the second sub-lens groupframe 54 includes a sealed region in the rear end portion thereof. Sincethe front end portion of the first sub-lens group frame 53 and the rearend portion of the second sub-lens group frame 54 do not overlap eachother, sliding of the sub-lens group frames with respect to one anotheris not affected.

Since the first sub-lens group frame 53 and the second sub-lens groupframe 54 are moved relative to one another in the optical axis directionto switch between the mutually close position and the mutually distantposition, the distances V1 and V2 between the first sub-lens group S1and the second sub-lens group S2 are uniquely determined not only by thesub-lens group contact surfaces 53 m and 54 m but also by the accuracyof the determining device for determining positions of the firstsub-lens group frame 53 and the second sub-lens group frame 54 in theoptical axis direction when they assume the mutually close position orthe mutually distant position. As described above, the follower engagingrecesses 53 e and 53 f formed on the rear end surface of the firstsub-lens group frame 53, together with the follower projections 54 aformed on the front end surface of the second sub-lens group frame 54,serve as the determining device for determining relative positions ofthe first sub-lens group frame 53 and the second sub-lens group frame 54in the present embodiment. In other words, the mutually close positionand the mutually distant position of the first sub-lens group frame 53and the second sub-lens group frame 54 are determined by the directengagement of the first sub-lens group frame 53 with the second sub-lensgroup frame 54.

Thus, the distances V1 and V2 between the first sub-lens group S1 andthe second sub-lens group S2 are not affected by the accumulation oftolerances in lens thickness in the lens barrel of the presentembodiment since all the elements necessary to determine the distancesV1 and V2 are included in the initial formation of the first sub-lensgroup frame 53 and the second sub-lens group frame 54. In other words, apredetermined distance can be obtained between the first sub-lens groupS1 and the second sub-lens group S2 by simply engaging the firstsub-lens group frame 53 with the second sub-lens group frame 54 afterthe first sub-lens group S1 and the second sub-lens group S2 have beenplaced into the first sub-lens group frame 53 and the second sub-lensgroup frame 54, respectively. In this manner, little deviation resultsin the distances V1 and V2 in different lens barrels. Thus, adjustmentmechanism for eliminating the deviation in the distances V1 and V2 inthe lens barrels can be dispensed with and a simple support structurefor the switching lens group 10 can be achieved.

As the actuator ring 55 is rotated, the first sub-lens group S1 and thesecond sub-lens group S2, when in the mutually distant position on thewide-angle side, are moved in the optical axis direction whilemaintaining the distance V1 defined by the first sub-lens group frame 53and the second sub-lens group frame 54 to provide focusing while thefirst sub-lens group S1 and the second sub-lens group S2, when in themutually close position on the telephoto side, are moved in the opticalaxis direction while maintaining the distance V2 defined by the firstsub-lens group frame 53 and the second sub-lens group frame 54 toprovide focusing. According to the lens support structure of the presentinvention, deviation from one lens barrel to another in positions of thesub-lens groups S1 and S2 upon focusing is avoided.

As can be understood from the above description, the present inventionprovides a lens barrel with simple construction which can preventdeviation in the distance between the first and the second sub-lensgroups that are optically operable when in the mutually close positionand in mutually distant position.

However, the present invention is not limited to the illustratedembodiment. For example, while the openings of the first and the secondsub-lens group frames 53 and 54 for inserting the first and the secondsub-lens groups S1 and S2 are heat-sealed after the sub-lens groups S1and S2 have been placed in the first and the second sub-lens groupframes 53 and 54 in the above-described embodiment, rings may be securedto the openings for preventing the lens groups from coming out.

Furthermore, obvious changes may be made in the specific embodiments ofthe present invention described herein, such modifications being withinthe spirit and scope of the invention claimed. It is indicated that allmatter contained herein is illustrative and does not limit the scope ofthe present invention.

What is claimed is:
 1. A lens barrel comprising: a front sub-lens groupprovided on the object side and a rear sub-lens group provided on theimage side, said front and rear sub-lens groups functioning opticallywhen in a mutually close position and in a mutually distant positionwith respect to the optical axes of said front and rear sub-lens groups;a front sub-lens group frame for supporting said front sub-lens groupand a rear sub-lens group frame for supporting said rear sub-lens group;a lens frame shift mechanism for causing said front sub-lens group frameand said rear sub-lens group frame to move relative to each other toobtain said mutually close position and said mutually distant position;a first lens group positioning surface, provided on said front sub-lensgroup frame, for positioning said front sub-lens group in the opticalaxis direction by contacting a portion of a rear surface of said frontsub-lens group upon said front sub-lens group being inserted from thefront side of said front sub-lens group frame; a front frame engagingportion provided on a rear side of said front sub-lens group frame, asecond lens group positioning surface, provided on said rear sub-lensgroup frame, for positioning said rear sub-lens group in the opticalaxis direction by contacting a portion of a front surface of said rearsub-lens group upon said rear sub-lens group being inserted from therear side of said rear sub-lens group frame; and a rear frame engagingportion provided on a front side of said rear sub-lens group frame,wherein said front frame engaging portion is held in engagement withsaid rear frame engaging portion in the direction of the optical axiswhile said front and rear sub-lens group frames are able to move in theoptical axis direction relative to each other.
 2. The lens barrelaccording to claim 1, wherein said front sub-lens group frame includes afront sealed region in the front end portion thereof, said front sealedregion preventing said front sub-lens group from coming out from thefront side of said front sub-lens group frame; and wherein said rearsub-lens group frame includes a rear sealed region in the rear endportion thereof, said rear sealed region preventing said rear sub-lensgroup from coming out from the rear side of said rear sub-lens groupframe.
 3. The lens barrel according to claim 1, further comprising: apair of follower engaging recesses which are formed on one of said frontframe engaging portion of said front sub-lens group frame and said rearframe engaging portion of said rear sub-lens group frame; and a followerprojection formed on the remaining one of said front frame engagingportion of said front sub-lens group frame and said rear frame engagingportion of said rear sub-lens group frame; wherein said mutually closeposition of said front sub-lens group is defined via engagement of saidfollower projection and one of said pair of follower engaging recesses,and said mutually distant position of said front sub-lens group isdefined via engagement of said follower projection and the other of saidpair of follower engaging recesses.
 4. The lens barrel according toclaim 1, wherein said front sub-lens group frame and said rear sub-lensgroup frame can be rotated relative to each other; and wherein said lensframe shift mechanism includes a shift cam mechanism provided on saidfront frame engaging portion of said front sub-lens group frame and saidrear frame engaging portion of said rear sub-lens group frame for movingsaid front and rear sub-lens group frames to said mutually distantposition and to said mutually close position in accordance with therelative rotation of said front and rear sub-lens group frames.
 5. Thelens barrel according to claim 4, wherein said shift cam mechanismincludes: a shift cam surface provided on one of the front frameengaging portion of said front sub-lens group frame and said rear frameengaging portion of said rear sub-lens group frame, said shift camsurface being inclined with respect to a circumferential directionthereof; and a follower projection provided on the remaining one of saidfront frame engaging portion of said front sub-lens group frame and saidrear frame engaging portion of said rear sub-lens group frame forengaging with said shift cam surface.
 6. The lens barrel according toclaim 5, wherein a pair of follower engaging recesses are formed atopposite ends of each of said shift cam surfaces, wherein said followerprojection engages with one of said follower engaging recesses when saidfront and rear sub-lens group frames are in said mutually close positionand in said mutually distant position.
 7. The lens barrel according toclaim 1, wherein said front and rear sub-lens groups form one of aplurality of variable lens groups of a zoom lens system that are movedin the optical axis direction during zooming, said front and rearsub-lens groups serving as a focusing lens group when in said mutuallyclose position and in said mutually distant position; and wherein saidlens barrel includes a focusing mechanism for moving said front and rearsub-lens group frames in said mutually close position and in saidmutually distant position, in the optical axis direction, whilemaintaining a constant distance between said front and rear sub-lensgroup frames.